Overall, I really did enjoy this show. I would give it a solid 8.5/10.

The acting was superb from the three main leads, especially Yoo Ah-in, who managed to portray his present and past self in ways that were distinctly different enough for the viewer to distinguish them emotionally and mourn for each of their struggles in turn.
Go Kyung-pyo was equally as sympathetic as Yoo Jin-Oh. [spoiler] I did cry over him the most, as Yul, despite understanding why and how his decisions in the end were made. [/spoiler]

Im Soo-jung and Kwak Si-yang, as Jeon Seol and Tae-Min, I was less enamored with. Perhaps it was the writing, but they were just not as strong of characters [spoiler] especially in comparison to their past selves.[/spoiler] Additionally, a lot of the supporting characters around the main trio were just not that interesting or emotionally compelling. [spoiler] We never got emotional closure on the issue of Jeon Seol's mother, or Bang-Jin and 'Ricardo' one sided love for example. ( I think it would have been cute if they got together, but maybe I am in the minority.) And I never felt completely sold on Mr Baek Do-Ha's actual love and support for Se-Joo when his wife actually tried to commit legitimate violence against a child in her care...and his son was a spoiled sociopath and he really didn't do anything about it. [/spoiler]

The music for this show? Perfectly executed, very poignant. I also appreciated the costuming/tailoring, especially for the Joseon flashbacks.

I did get frustrated with the pacing in some places, twists were drawn out for too long and thereby lost their emotional impact. I had long figured out who-done-what before the big reveal.

Overall, I am glad I caught this on Netflix before being removed at the end of the month. It is still available on Viki though, and is worth the watch.